1. Field of the Invention
The present invention relates to a polarographic sensor for monitoring lactic acid and lactate levels in the vascular system, and in particular to a polarographic sensor incorporated on a catheter to permit the in vivo study of lactate metabolism at a specific site in a mammal body.
2. Description of the Prior Art
The role of lactate as the most reliable metabolic indicator of anaerobiosis has long been appreciated in physiology and clinical medicine. Lactate is currently regarded as the best single measurement for the immediate diagnosis, quantitation of the severity, and prognosis of shock states. It is also an indicator of prognosis in acute myocardial infarction and myocardial failure. In sports medicine and exercise physiology, blood lactate levels measure anaerobic capacity and can be used to evaluate the effectiveness of training, predict endurance and detect over-training.
For many years it has been known in the art that enzyme-coupled electrodes are useful for polarographic analysis of certain substances. For example, U.S. Pat. No. 3,539,455 discloses the membrane polarographic electrode system method for the rapid and accurate quantitative analysis of glucose levels in blood. U.S. Pat. No. 4,356,074 discloses an invention wherein the relative specificity of the enzyme galactose oxidase for various substrate materials to be determined polarographically is controlled as a function of a redox potential applied to the enzyme. U.S. Pat. No. 4,404,066 discloses an invention wherein any multisubstrate enzyme having a redox potential resulting in a direct activity dependent upon potential may be controlled wherein the relative activity of the enzyme formed in an enzyme electrode is controlled as a function of a redox potential applied to the enzyme.
In addition, recent advances have been made for analyzing lactic acid and lactate levels. In U.S. Pat. No. 4,005,002 and U.S. Pat. No. 4,129,478, Racine et al. disclose a method based on the highly specific oxidation of lactate to pyruvate in the presence of the enzyme cytochrome b.sub.2 and hexacyanoferrate-(III). Also, U.S. Pat. No. 4,166,763 discloses an enzyme for use in analysis of lactic acid whereby the lactic acid is oxidized to produce pyruvate and hydrogen peroxide. The hydrogen peroxide is then measured colorometrically. These methods are all time consuming and expensive and fail to provide a means to rapidly detect lactic acid directly.
Clark has described a method for directly measuring lactic acid and lactate levels by means of a polarographic analysis in U.S. Pat. No. 4,467,811. However, Clark's invention requires that a sample of blood be taken and injected into a reaction chamber where the process takes place in vitro.
There is a genuine need in the art to provide an in vivo method which can continuously and instantaneously monitor lactic acid and lactate concentrations at specific sites in mammal bodies.